Hey Nic,
I’m not really sure how to proceed here. I have Divi version 3.0.14 installed on my test site and the comments are showing fine. I also checked our logged bug reports but am not finding anything relative to your issue.

While theme conflicts are typically outside the scope of support, we have a fair amount of Divi users. Is there any way you can send a .zip file of the latest version and if I can reproduce the conflict I’ll get a bug logged for the developers to review. I can’t promise anything on our end but am happy to update you once I hear back from the developers.
Let me know and we’ll go from there. Cheers 🙂